Explosive compounds with reduced sensitivity characteristics are desirable to provide safe loading, packing and assembly operations, in particular for military applications. The two most widely used explosive compounds, Research Department Composition X (RDX) (1,3,5-Trinitro-1,3,5-triazacyclohexane, also known as cyclotrimethylene trinitramine) and High Molecular Weight RDX (HMX) (1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane, also known as cyclotetramethylene tetranitramine), each have properties sought for modern munitions. Pure RDX is relatively insensitive and desirable for that characteristic while HMX is not. RDX may be produced several ways, the most common being the continuous Bachmann Process that involves reacting hexamine with nitric acid, ammonium nitrate, glacial acetic acid, and acetic anhydride. Bachmann et al., J. Am. Chem. Soc., 71, 1842, (1979). The resultant product is filtered and re-crystallized to form RDX containing a typically acceptable 8-12% HMX. L. A. Nock and R. Doherty, Reduced Sensitivity RDX: US and International Efforts, 39th Annual Gun & Ammunition/Missiles & Rockets Conference 7 Exhibition, Baltimore, Md., 13-16 Apr. 2004. The sensitivity of the final product depends on the relative proportions of RDX and HMX, sensitivity generally increasing with increased HMX. HMX, along with solvent inclusions, is the main impurity causing increased sensitivity. Lionel Borne and Helmut Ritter, HMS as an Impurity in RDX Particles: Effect on the Shock Sensitivity of Formulations Based on RDX; Propellants, Explosives, Pyrotechnics., 31, 482, 2006. Thus, to increase RDX content and reduce sensitivity of the resultant RDX product, a better method is required to selectively eliminate HMX from the initially formed RDX/HMX combination.
Attempts yielding marginal success in reducing the amount of HMX in the initial formulation of RDX included simple re-crystallization by freezing; selective adsorption of RDX or HMX on various sorbents (e.g., granular activated carbon (GAC), XAD™ resins, alginates, and the like), membrane separation; and phase separation by adding a hydrophilic solvent.
A goal met by select embodiments of the present invention is purifying an initial product having about 90% RDX and about 10% HMX to a final product having greater than about 99% RDX depending on the desired yield percentage.